Ligand Graft Functionalized Substrates

ABSTRACT

Polyethyleneimine and polyalkylene biguanide ligand functionalized substrates, methods of making ligand functionalized substrates, and methods of using functionalized substrates are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of priority to U.S.provisional patent application Ser. No. 61/098,337 entitled “LIGANDGRAFT FUNCTIONALIZED SUBSTRATES”, filed on Sep. 19, 2008, the subjectmatter of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to ligand-functionalized substrates, andmethods for preparing the same. The functionalized substrates are usefulin selectively binding and removing biological materials, such asviruses, from biological samples.

BACKGROUND

Detection, quantification, isolation and purification of targetbiomaterials, such as viruses and biomacromolecules (includingconstituents or products of living cells, for example, proteins,carbohydrates, lipids, and nucleic acids) have long been objectives ofinvestigators. Detection and quantification are importantdiagnostically, for example, as indicators of various physiologicalconditions such as diseases. Isolation and purification ofbiomacromolecules are important for therapeutic and in biomedicalresearch. Biomacromolecules such as enzymes which are a special class ofproteins capable of catalyzing chemical reactions are also usefulindustrially; enzymes have been isolated, purified, and then utilizedfor the production of sweeteners, antibiotics, and a variety of organiccompounds such as ethanol, acetic acid, lysine, aspartic acid, andbiologically useful products such as antibodies and steroids.

In their native state in vivo, structures and corresponding biologicalactivities of these biomacromolecules are maintained generally withinfairly narrow ranges of pH and ionic strength. Consequently, anyseparation and purification operation must take such factors intoaccount in order for the resultant, processed biomacromolecule to havepotency.

Chromatographic separation and purification operations can be performedon biological product mixtures, based on the interchange of a solutebetween a moving phase, which can be a gas or liquid, and a stationaryphase. Separation of various solutes of the solution mixture isaccomplished because of varying binding interactions of each solute withthe stationary phase; stronger binding interactions generally result inlonger retention times when subjected to the dissociation ordisplacement effects of a mobile phase compared to solutes whichinteract less strongly and, in this fashion, separation and purificationcan be effected.

Most current capture or purification chromatography is done viaconventional column techniques. These techniques have severebottlenecking issues in downstream purification, as the throughput usingthis technology is low. Attempts to alleviate these issues includeincreasing the diameter of the chromatography column, but this in turncreates challenges due to difficulties of packing the columnseffectively and reproducibly. Larger column diameters also increase theoccurrence of problematic channeling. Also, in a conventionalchromatographic column, the absorption operation is shut down when abreakthrough of the desired product above a specific level is detected.This causes the dynamic or effective capacity of the adsorption media tobe significantly less than the overall or static capacity. Thisreduction in effectiveness has severe economic consequences, given thehigh cost of some chromatographic resins.

Polymeric resins are widely used for the separation and purification ofvarious target compounds. For example, polymeric resins can be used topurify or separate a target compound based on the presence of an ionicgroup, based on the size of the target compound, based on a hydrophobicinteraction, based on a specific receptor-ligand affinity interaction,or based on the formation of a covalent bond, or a combination of theaforementioned interactions. There is a need in the art for polymericsubstrates having enhanced affinity for viruses to allow efficientremoval from a biological sample. There is further need in the art forligand functionalized membranes that overcome limitations in diffusionand binding, and that may be operated at high throughput and at lowerpressure drops.

SUMMARY OF THE INVENTION

The present invention is directed to ligand functionalized substrates,preferably porous substrates, and methods of making the same. Morespecifically, the functionalized substrates include a base substrate,preferably a porous base substrate, which has been modified to providegrafted ligand groups having the requisite specific binding capacity forbinding charged biomaterials, such as viruses. The ligand functionalizedsubstrate may be described as the grafted reaction product of asubstrate and a ligand compound of Formulas I or II:

wherein each R⁴ is individually H, alkyl or aryl,each R⁶ is individually alkylene or arylene,c may be zero or an integer from 1 to 500, andd is zero or 1, with the proviso that when d is zero, then c is 1 to500;or

wherein x may be zero, y is at least 1, and x+y is 2 to 2000.

Methods of making a ligand functionalized substrate are provided. Themethods may comprise:

providing a substrate, preferably a porous substrate, that may be athermoplastic or a polysaccharide polymer;

grafting an electrophilic functional group to the surface of thesubstrate to produce a substrate having grafted electrophilic functionalgroups extending from the surface(s) thereof; and

reacting the grafted electrophilic groups with a ligand compound ofFormulas I and/or II to produce a substrate having grafted ligand groupsextending from the surface(s) of the substrate.

In some embodiments, the substrate polymer has surface functional groupsto which a grafting compound may be attached. Grafting compounds have afirst functional group that is reactive toward the surface functionalgroups of the substrate polymer, and a second electrophilic functionalgroup that is reactive to an amine (or imine) of the ligand compounds.For example, polysaccharide substrates have hydroxyl groups which may bereacted with a grafting compound by addition, condensation ordisplacement reactions with a grafting compound to provide a grafted,reactive electrophilic functional group for subsequent reaction with theligand compound.

In other embodiments, the substrate polymer has no such surfacefunctional groups; polymers such as polypropylene may either be exposedto plasma discharge to provide surface hydroxyl groups that may be usedto react with the grafting compound. Alternatively, polymers such aspolypropylene may be grafted with ethylenically unsaturated graftingmonomers having an ethylenically unsaturated group for ionizingradiation-initiated grafting to provide free radical to the polymersurface and a second reactive electrophilic functional group forsubsequent reaction with the ligand compounds.

An article is provided comprising a substrate, preferably a poroussubstrate having interstitial and outer surfaces, and grafted biguanideligand groups extending from the surfaces thereof, the ligand groupsderived from ligand compound of Formula I, the grafted biguanide ligandgroups corresponding to one or more of Formulas III to VIII, where R²and a are as previously defined. For illustration, only biguanidecompounds are shown. Similar linkages are formed with bis-biguanide andpoly(biguanide) compounds.

The preparation of biguanide, bis-biguanide and poly(biguanide)compounds of Formula I are known in the art. Reference may be made to F.H. S. Curd and F. L. Rose, J. Chem. Soc., 1946, 729-737, O′Malley etal., J. Appl. Microbiol. 103: 1158, 2007 and East et al., Polymer,38:3973, 1997 which describe the synthesis of many biguanides. Thesynthesis of bis-biguanides is discussed by F. L. Rose and G. Swain, J.Chem. Soc., 1956, 4422-4425. It will be understood that the preparationof biguanides with an amine and dicyanoamine may yield a complex mixtureof products which includes those of Formula I. In particular, thebiguanides may have terminal or pendant cyano groups.

Alternately, an article is provided comprising a substrate, preferably aporous substrate having interstitial and outer surfaces, and graftedligand groups extending from the surfaces thereof, the ligand groupsderived from a ligand compound of Formula II, the grafted ligand groupscorresponding to one or more of Formulas IX to XII, where x and y are aspreviously defined.

Alternatively, with respect to the ligand compound of Formula II, thegrafted ligand group may be depicted as having repeat units of theformulas:

where each of x and y may be zero or a non-zero value, and x and/or y isat least 2. The indicated repeat units are grafted to the substratesurface through one or more of the nitrogen atoms, as depicted supra. Itwill be understood that the preparation of polyalkyleneimines yield acomplex mixture of products that may include both linear and branchedpolymers, and which may be random, block or alternating copolymers ofthe units supra, or more complex branched mixtures.

With respect to the above Formulas III to XII, the “˜” represents acovalent bond or an organic linking group interposed between the ligandgroup and the surface of the base substrate. The linking grouprepresents the residue of the grafting monomer or grafting compound. Thearticle may further comprise grafted ionic or hydrophilic groupsextending from the surfaces of the substrate.

These and other features and advantages of the present invention willbecome apparent after a review of the following detailed description ofthe disclosed embodiments and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

In the article and methods of this disclosure, ligand-functionalizedarticles are provided by a process of functionalizing of the substrateby grafting and subsequent reaction of the graft-functionalizedsubstrate with a ligand compound of Formulas I and II and optionally anionic or hydrophilic compound or an ionic or hydrophilic graftingmonomer. Compared to the base substrate before surface modification, theligand functionalized substrate typically has enhanced bindingselectivity for charged biological materials such as host cell proteins,DNA, RNA and viruses. The binding selectivity for such biomaterialsallows positively charged materials, such as antibodies to be passed, asthey are not bound to the ligand functional groups. The ligandfunctionalized substrate allows the selective capture or binding oftarget biomaterials by the ionic interaction between target biomoleculesand the ligand groups, while other materials, lacking the specificbinding interactions for the ligand groups are passed.

The ligand functionalized substrate comprises a number of componentsincluding, but not limited to, (1) a base substrate, and (2) thereaction product of (a) a grafted reactive electrophilic functionalgroup extending from the surfaces of the base substrate, with (b) one ormore ligand compounds of Formulas I or II. The reaction productcorresponds to one or more of Formulas III to XII. Preferably the basesubstrate is a porous base substrate having interstitial and outersurfaces. The substrate may be a thermoplastic polymer or apolysaccharide polymer.

In one embodiment, the substrate comprises a polysaccharide. The term“polysaccharide” includes compounds made up of many, hundreds orthousands, of monosaccharide units per molecule connected by glycosidelinkages. Their molecular weights are normally higher than about 5,000and can range up to millions of daltons. They are normally naturallyoccurring polymers, such as, for example, starch, glycogen, cellulose,gum arabic, agar, and chitin. The polysaccharide should have one or morereactive hydroxy groups. It may be straight or branched chain. The mostuseful of the polysaccharides for the purposes of this invention iscellulose.

The polysaccharide is preferably fully unprotected and carries all ofits hydroxy groups in the free state. Some blocking of the hydroxygroups is possible, as for example, by acylation or aminoacylation.Extensive blocking of the hydroxy groups of the polysaccharide, however,is undesirable since the polysaccharide thereby loses its hydrophiliccharacter, which provides appropriate chemically compatible interactionwith biomolecules. If the polysaccharide becomes too hydrophobic,negative interactions with such molecules as proteins lead to possiblenonspecific bonding and denaturation phenomena. Also, if the masking ofthe polysaccharide hydroxy groups is too extensive, the reactivity ofthe polymer is greatly diminished. For all of these reasons, it ispreferred to retain substantially all hydroxy groups in the free state.The polysaccharide is chemically activated by the reactive functionalgroups described herein.

Cellulose is the preferred polysaccharide. By “cellulose” it is intendedto mean any of the convenient and commercially available forms ofcellulose such as wood pulp, cotton, hemp, ramie, or regenerated formssuch as rayon. There exists no criticality as to the selection of asuitable form of cellulose. Cellulose is a naturally occurringpolysaccharide consisting of beta 1,4 linked glucose units. In thenative state, adjacent cellulose chains are extensively hydrogen-bonded,forming microcrystalline regions. These regions are interspersed byamorphous regions with less hydrogen bonding. Limited acid hydrolysisresults in preferential loss of the amorphous regions and givesso-called microcrystalline cellulose. The cellulose useful in thepresent invention is either cellulose in the native state or in themicrocrystalline state. Also, cellulose derived from cotton linter maybe preferable to that derived from wood pulp, as the latter containslignin.

Chemical reactions to attach the ligand groups to the polysaccharidematerial normally proceed with difficulty in crystalline regions buttake place more readily in amorphous regions. For example, thesubstitution of functional groups into cellulose has a disruptive effecton the structure thereof. If carried out to completion, the cellulosematrix would be destroyed and ultimately water-soluble polymers would beformed. Typical examples of this phenomenon are the hydroxyethylcellulose and cellulose gums of the prior art, which become the commonlyused adhesives and binders after dissolving in water.

Each saccharide unit in a polysaccharide molecule may have three or morereactive hydroxy groups. All or a portion of the hydroxyl groups may besubstituted with the ligand group. The product from such reaction,however, would have a degree of substitution of three or more, which incase of ion-exchange materials, may denature the polymer. Even at lowerlevels of substitution below those at which total water solubilityoccurs, such polysaccharide derivatives may become unsuitable aschromatographic supports. Therefore, substitution of the polysaccharideis desirably restricted to the more reactive centers of the amorphousregions and is seldom carried out beyond the level of about 1 mEQ/gm ofdry weight of the saccharide polymer. At this level of substitution, thenative configuration of the polysaccharide structure is only slightlymodified, and the low-density, non-uniform exchange sites are readilyaccessible to large biomolecules.

The final structure of a molecular support of the invention thuscomprises a polysaccharide chain covalently graft-modified at amultiplicity of sites along such chain with the ligand groups.

The substrate may be in any form such as films or sheets. Preferably thesubstrate (e.g., the polysaccharide substrate) is porous, which include,but are not limited to, porous membranes, porous nonwoven webs, andporous fibers. The substrate could be made by a number of methods,including casting from solvent, wet laid fibers, or dry laid fibers.

In another embodiment, the substrate may be formed from any suitablethermoplastic polymeric material. Suitable polymeric materials include,but are not limited to, polyolefins, poly(isoprenes), poly(butadienes),fluorinated polymers, chlorinated polymers, polyamides, polyimides,polyethers, poly(ether sulfones), poly(sulfones), poly(vinyl acetates),copolymers of vinyl acetate, such as poly(ethylene) co-poly(vinylalcohol), poly(phosphazenes), poly(vinyl esters), poly(vinyl ethers),poly(vinyl alcohols), and poly(carbonates).

In some embodiments, the thermoplastic polymer may be surface treated,such as by plasma discharge, to provide suitable functionality to thesurface of the substrate. Surface treatment provides functional groupssuch as hydroxyl groups, enabling grafting with a grafting compound andsubsequent reaction with a ligand compound. One such useful plasmatreatment is described in U.S. Pat. No. 7,125,603 (David et al.).

Suitable polyolefins include, but are not limited to, poly(ethylene),poly(propylene), poly(1-butene), copolymers of ethylene and propylene,alpha olefin copolymers (such as copolymers of ethylene or propylenewith 1-butene, 1-hexene, 1-octene, and 1-decene),poly(ethylene-co-1-butene) and poly(ethylene-co-1-butene-co-1-hexene).

Suitable fluorinated polymers include, but are not limited to,poly(vinyl fluoride), poly(vinylidene fluoride), copolymers ofvinylidene fluoride (such as poly(vinylidenefluoride-co-hexafluoropropylene), and copolymers ofchlorotrifluoroethylene (such aspoly(ethylene-co-chlorotrifluoroethylene).

Suitable polyamides include, but are not limited to,poly(iminoadipolyliminohexamethylene),poly(iminoadipolyliminodecamethylene), and polycaprolactam. Suitablepolyimides include, but are not limited to, poly(pyromellitimide).

Suitable poly(ether sulfones) include, but are not limited to,poly(diphenylether sulfone) and poly(diphenylsulfone-co-diphenyleneoxide sulfone).

Suitable copolymers of vinyl acetate include, but are not limited to,poly(ethylene-co-vinyl acetate) and such copolymers in which at leastsome of the acetate groups have been hydrolyzed to afford variouspoly(vinyl alcohols).

A preferred substrate is a porous substrate that is a hydrophilicmicroporous membrane such as a thermally-induced phase separation (TIPS)membrane. TIPS membranes are often prepared by forming a solution of athermoplastic material and a second material above the melting point ofthe thermoplastic material. Upon cooling, the thermoplastic materialcrystallizes and phase separates from the second material. Thecrystallized material is often stretched. The second material isoptionally removed either before or after stretching. Microporousmembranes are further disclosed in U.S. Pat. No. 4,529,256 (Shipman);U.S. Pat. No. 4,726,989 (Mrozinski); U.S. Pat. No. 4,867,881 (Kinzer);U.S. Pat. No. 5,120,594 (Mrozinski); U.S. Pat. No. 5,260,360(Mrozinski); and U.S. Pat. No. 5,962,544 (Waller, Jr.). Some exemplaryTIPS membranes comprise poly(vinylidene fluoride) (PVDF), polyolefinssuch as poly(ethylene) or poly(propylene), vinyl-containing polymers orcopolymers such as ethylene-vinyl alcohol copolymers andbutadiene-containing polymers or copolymers, and acrylate-containingpolymers or copolymers. For some applications, a TIPS membranecomprising PVDF is particularly desirable. TIPS membranes comprisingPVDF are further described in U.S. Pat. No. 7,338,692 (Smith et al.).

The base substrate may be in any form such as films or sheets.Preferably the base substrate is porous. Suitable porous base substratesinclude, but are not limited to, porous membranes, porous nonwoven webs,and porous fibers.

In many embodiments, the base substrate has an average pore size that istypically greater than about 0.2 micrometers in order to minimize sizeexclusion separations, minimize diffusion constraints and maximizesurface area and separation based on binding of a target molecule.Generally, the pore size is in the range of 0.1 to 10 micrometers,preferably 0.5 to 3 micrometers and most preferably 0.8 to 2 micrometerswhen used for binding of viruses. The efficiency of binding other targetmolecules may confer different optimal ranges.

The functionalized substrate, whether thermoplastic or polysaccharide,has grafted groups attached to the surfaces of the base substrate whichincludes a) at least one ligand group, with b) optionally one or morehydrophilic groups and/or ionic groups.

The substrate, having a reactive group thereon is further reacted with aligand compound to provide the ligand groups grafted to the surface(s)of the substrate.

In another embodiment, the ligand compound is of the formula:

wherein each R⁴ is individually H, alkyl or aryl,each R⁶ is individually alkylene or arylene,c may be zero or an integer from 1 to 500, preferably at least 5, morepreferably 5-500; andd is zero or 1, with the proviso that when d is zero, then c is 1 to500;or

wherein x and y are at least 1, and x+y is 2 to 2000. When grafted tothe surface of the substrate, the grafted ligand groups may berepresented by the Formulae III to XII (supra).

The above-described ligand functionalized substrates may be preparedusing a combination of process steps. In some embodiments, the methodcomprises:

providing a substrate, preferably a porous substrate that may be athermoplastic or a polysaccharide polymer, grafting an electrophilicfunctional group to the surface of the substrate, with a graftingcompound or grafting monomer, to produce a substrate having graftedelectrophilic functional groups extending from the surface(s) thereof;and

reacting the grafted electrophilic functional group with a ligandcompound of Formula I or II to produce a substrate having grafted ligandgroups extending from the surface(s) of the substrate as depicted inFormulas III to XII.

In one embodiment, the method comprises:

1) providing a base polysaccharide substrate, preferably a porous basesubstrate, having interstitial and outer surfaces;

2) grafting the base polysaccharide substrate by contacting with agrafting compound having a first functional group reactive with thehydroxyl groups of the polysaccharide substrate and second functionalgroup to produce a surface modified polysaccharide substrate havinggrafted second functional groups, said second grafted functional groupsbeing either electrophilic functional groups, or groups that may beconverted to electrophilic functional groups; and

3) subsequently contacting the surface modified polysaccharide substratehaving grafted electrophilic functional groups with a ligand compound ofFormulas I and/or II.

In one embodiment, the grafting compound of step two has a secondelectrophilic functional group that is reactive with the amine (orimine) groups of the ligand compound. In a second embodiment, thegrafting compound has a functional group that may be converted to anelectrophilic functional group reactive with the amine group of theligand compound. For example, the polysaccharide substrate may first bereacted with allyl glycidyl ether, wherein the epoxy group is reactivetoward the hydroxy groups of the polysaccharide polymer. The resultantgrafted allyl groups however, are not reactive toward the amine group ofthe ligand compound, but may be reacted with N-bromosuccinimide orbromine water to produce a terminal bromo group which is electrophilicand reactive (by nucleophilic displacement) with the amine (or imine)groups of the ligand compounds of Formulas I and II.

In one embodiment, the grafting compound has a group capable of reactingwith a hydroxy group of polysaccharide with the formation of a covalentbond. The chemical groups are capable of reacting with hydroxy groups attemperatures up to those at which the polysaccharide begins to decomposeor depolymerize, e.g., 0° to 120° C., in aqueous solution and therebyform covalent bonds with the hydroxy groups. Since water may be presentin considerable excess with respect to the hydroxy groups of thepolysaccharide, chemical groups which react spontaneously with water,such as, for example, isocyanate groups, are less suitable.

Hydroxy reactive groups of the grafting compound may be activatedcarboxy groups such as are known from peptide chemistry or O-alkylatingagents, such as alkyl halide or epoxide groups. Representatives of theO-alkylating comonomers are acrylic and methacrylic anhydrides,acrylolyl or methacrylol N-hydroxy succinimides, Q-halo-alkyl esters ofacrylic or methacrylic acid in which the alkyl group in general containstwo to six carbon atoms, allyl halides, chloromethylstyrene,chloroacetoxy allyl ether, and compounds having a glycidyl group. Thelatter are ethers or esters formed between a glycidyl alcohol and anunsaturated alcohol or unsaturated carboxylic acid, respectively. Theglycidyl alcohols are aliphatic and cycloaliphatic alcohols and etheralcohols having from 3 to 18 carbon atoms which are esterified with anα,β-unsaturated carboxylic acid, preferably acrylic or methacrylic acid,or are etherified with an olefinically or acetylenically unsaturatedalcohol. Typical compounds are glycidyl acrylate and methacrylate;4,5-epoxy-pentylacrylate; 4-(2,3-epoxy-propyl)-N-butyl-methacrylate;9,10-epoxy-stearylacrylate; 4-(2,3-epoxypropyl)-cyclohexylmethylacrylate; ethylene glycol-monoglycidyl etheracrylate; and allylglycidyl ether.

Other useful grafting compounds that may be used to graft to the surfaceof the polysaccharide substrate include cyanuric chloride,N-hydroxysuccinimide esters, the multi-functional compounds withterminal acyl sulfonamide groups as described in U.S. Pat. No. 7,402,678(Benson et al.), the halo phosphonitrile compounds described in U.S.2005/0142296A (Lakshmi et al.), triazine compounds as described in U.S.2007/0065490 (Schaberg et al.), the N-sulfonyldicarboximide compoundsdescribed in U.S. Pat. No. 7,361,767 and U.S. Pat. No. 7,169,933 (Bensonet al.)

In some embodiments, the polysaccharide substrate further comprisesgrafted ionic groups such as quaternary ammonium groups. Such groups maybe grafted by contacting the polysaccharide substrate withepichlorohydrin and base, react with a tertiary amine, or a secondaryamine followed by alkylation. Alternatively, quaternary ammonium groupsmay be grafted to the surface of the substrate by reaction withglycidyltrimethylammonium chloride. In some embodiments, thepolysaccharide substrate further comprises grafted hydrophilic groups,such as poly(ethylene oxide) groups, which may be grafted by reaction ofthe substrate with a compound such as poly(ethylene oxide) mono- ordiacid.

Other polymers, lacking functional groups such as the hydroxyl groups ofpolysaccharides, are advantageously functionalized with an ionizingradiation grafting technique. In this embodiment, thermoplasticpolymers, such as polypropylene or polyvinylidene fluoride (PVDF), arefirst grafted with a grafting monomer, and subsequently reacted with theligand compound of Formulas I or II. The grafting monomers have anethylenically unsaturated group which, when exposed to ionizingradiation in the presence of the substrate leads to a radical-initiatedcovalent attachment to the surface of the substrate. As result, thesubstrate is functionalized with the grafting monomer.

The functionalized substrate has grafted species, the grafting monomer,attached to the surfaces of the base substrate. The grafting of graftingmonomers to the surface of the porous base substrate results in theattachment of a functional group that is reactive with an amine (orimine) group of the ligand compounds or Formulas I and II. This aminegroup may be present on the terminus of the ligand compound, such as aprimary amine or may be present in the interior of the ligand compound,such as a secondary amine, or as a primary amine on a branching moiety.The grafting monomers have both (a) a free-radically polymerizable groupand (b) at least one additional second functional group thereon. Theadditional second functional group of the grafting monomer may be anelectrophilic group, or another functional group that may be convertedto an electrophilic group.

The free-radically polymerizable group is typically an ethylenicallyunsaturated group such as a (meth)acryloyl group or a vinyl group. Thefree-radically polymerizable group typically can react with the surfaceof the porous base substrate when exposed to an electron beam or otherionizing radiation. That is, reaction of the free-radicallypolymerizable groups of the grafting monomers with the surface of theporous base substrate in the presence of the electron beam results inthe formation of grafted species attached to the porous base substrate.One or more grafting monomers may be grafted onto interstitial and outersurfaces of the porous base substrate.

In addition to having a free-radically polymerizable group, suitablegrafting monomers have an additional functional group such as an epoxygroup, an azlactone group, an isocyanato group, a halo group, that isreactive toward the amine group of the ligand compound, or can befurther activated to be reactive toward the amine group of the ligandcompounds such as an allyl group. That is, after the grafting monomerhas been attached to the porous base substrate through a reactioninvolving the free-radically polymerizable group, the additionalfunctional group of the resulting grafted species can be reacted furtherwith the ligand compound.

In addition, optional grafting monomers may have functional groups usedto provide further reactivity, or binding specificity for particularanalytes (or which would retard binding of other analytes) such as anionic group, a second ethylenically unsaturated group, an alkylene oxidegroup, or a hydrophobic group. In these instances, the additionalfunctional group can impart a desired surface property to thefunctionalized substrate such as affinity for a particular type ofcompound. If the grafted species contains an ionic group, thefunctionalized substrate will often have an affinity for compoundshaving an opposite charge. That is, compounds with negatively chargedgroups can be attracted to a functionalized substrate having graftedspecies with a cationic group and compounds with positively chargedgroups can be attracted to a functionalized substrate having graftedspecies with an anionic group. Further, the grafted species can impart ahydrophilic surface to the functionalized substrate that includes aporous base substrate having a hydrophobic surface prior to surfacemodification with the grafted species. That is, the grafted speciescontain an alkylene oxide group can impart a hydrophilic character tothe resulting functionalized substrate.

Some grafting monomers have a) a first ethylenically unsaturated groupfor grafting to the surface of the substrate and b) an additionalfunctional group that is an epoxy group. Suitable grafting monomerswithin this class include, but are not limited to,glycidyl(meth)acrylates. This class of grafting monomers can provide afunctionalized substrate having at least one epoxy group available forfurther reactivity. The epoxy group can react with the ligand compound,which results in the opening of the epoxy ring and the formation of alinkage group that functions to attach the ligand compound to the porousbase substrate. The linkage group formed by ring-opening of the epoxygroup often contains the group —C(OH)HCH₂NH— when the epoxy is reactedwith a primary amino group of the ligand compound. The epoxy group canreact with other reactants such as another nucleophilic compound toimpart a desired surface property to the base substrate (e.g., bindingspecificity for a particular compound or functional group havingdifferent reactivity).

Other grafting monomers have a (a) free-radically polymerizable groupthat is an ethylenically unsaturated group and (b) an additionalfunctional group that is an azlactone group or a precursor to anazlactone group. Suitable grafting monomers include, but are not limitedto, vinyl azlactone such as 2-vinyl-4,4-dimethylazlactone andN-acryloyl-2-methylalanine. This class of grafting monomers can providea functionalized substrate having at least one azlactone group (or aprecursor to an azlactone group) available for further reactivity withthe ligand compound. The azlactone group can react with other reactantssuch as another monomer or with a nucleophilic compound to impart adesired surface property to the porous base substrate (e.g., bindingspecificity for a particular compound or functional group havingdifferent reactivity). The reaction of the azlactone group with a ligandcompound, for example, results in the opening of the azlactone ring andthe formation of a linkage group that functions to attach thenucleophilic compound to the porous base substrate. The linkage groupformed by ring-opening of the azlactone group often contains the groupCH₂═CH—(CO)NHC(R³)₂ (CO)— where R³ is an alkyl such as methyl.

In some embodiments, the azlactone groups can be reacted with amonofunctional amine such allyl amine wherein the amine group can reactby a ring opening reaction with the azlactone group and result in theformation of a linkage containing the groupCH₂═CH—(CO)NHC(R³)₂(CO)NH—CH₂—CH═CH₂. The grafted allyl group may thenbe converted to an electrophilic functional group for further reactionwith the ligand compounds of Formulas I and II. For example, theterminal allyl group may be brominated, by a suitable brominating agentsuch as N-bromosuccinimide to produce a terminal electrophilic bromide,which may then be reacted with the nucleophilic nitrogen atoms of theligand compounds of Formulas I and II to produce the pendant ligandgroups of Formulas III to XII.

In some embodiments, the azlactone groups can be reacted with amultifunctional amine such as a diamine having two primary amino groupsor a triamine having three primary amino groups. One of the amino groupscan react by a ring opening reaction with the azlactone group and resultin the formation of a linkage containing the group-(CO)NHC R³ ₂(CO)—between the nucleophilic compound and the base substrate. The secondamino group or second and third amino groups can import a hydrophiliccharacter to the functionalized substrate. In some examples, themultifunctional amine is a polyalkylene glycol diamine or a polyalkyleneglycol triamine and reaction with an azlactone group results in theattachment of a grafted species having a polyalkylene glycol group(i.e., polyalkylene oxide group). The polyalkylene glycol group as wellas any terminal primary amino group tends to impart a hydrophiliccharacter to the functionalized substrate.

Other grafting monomers have a (a) free-radically polymerizable groupthat is an ethylenically unsaturated group and (b) an additionalfunctional group that is an isocyanato group. Suitable grafting monomersinclude, but are not limited to an isocyanatoalkyl(meth)acrylate such as2-isocyanatoethyl methacrylate and 2-isocyanatoethyl acrylate. Thisclass of grafting monomers can provide a functionalized substrate havingat least one isocyanato group available for reactivity. The isocyanatogroup can react with other reactants such as the ligand compounds orwith a nucleophilic compound to impart a desired surface property to thefunctionalized substrate (e.g., affinity for a particular compound orfunctional group having different reactivity). The reaction of anisocyanato group with an amine group of the ligand compounds can resultin the formation of a urea linkage.

Yet other optional grafting monomers have a (a) free-radicallypolymerizable group that is an ethylenically unsaturated group and (b)an additional ionic functional group. The ionic group can have apositive charge, a negative charge, or a combination thereof. With somesuitable ionic monomers, the ionic group can be neutral or chargeddepending on the pH conditions. This class of monomers is typically usedto impart a desired surface binding specificity for one or moreoppositely charged compounds or to decrease the affinity for one or moresimilarly charged compounds.

Some exemplary ionic grafting monomers having a negative charge include,but are not limited to, N-acrylamidomethanesulfonic acid,2-acrylamidoethanesulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonicacid, and 2-methacrylamido-2-methyl-1-propanesulfonic acid. Salts ofthese acidic monomers can also be used. Counter ions for the salts canbe, for example, ammonium ions, potassium ions, lithium ions, or sodiumions.

Other suitable ionic grafting monomers having a negative charge includesulfonic acids such as vinylsulfonic acid and 4-styrenesulfonic acid;(meth)acrylamidophosphonic acids such as (meth)acrylamidoalkylphosphonicacids (e.g., 2-acrylamidoethylphosphonic acid and3-methacrylamidopropylphosphonic acid); acrylic acid and methacrylicacid; and carboxyalkyl(meth)acrylates such as 2-carboxyethylacrylate,2-carboxyethylmethacrylate, 3-carboxypropylacrylate, and3-carboxypropylmethacrylate. Still other suitable acidic monomersinclude (meth)acryloylamino acids, such as those described in U.S. Pat.No. 4,157,418 (Heilmann), incorporated herein by reference. Exemplary(meth)acryloylamino acids include, but are not limited to,N-acryloylglycine, N-acryloylaspartic acid, N-acryloyl-.beta.-alanine,and 2-acrylamidoglycolic acid. Salts of any of these acidic monomers canalso be used.

Some exemplary ionic grafting monomers that are capable of providing apositive charge are amino(meth)acrylates or amino(meth)acrylamides orquaternary ammonium salts thereof. The counter ions of the quaternaryammonium salts are often halides, sulfates, phosphates, nitrates, andthe like. Exemplary amino(meth)acrylates includeN,N-dialkylaminoalkyl(meth)acrylates such as, for example,N,N-dimethylaminoethylmethacrylate, N,N-dimethylaminoethylacrylate,N,N-diethylaminoethylmethacylate, N,N-diethylaminoethylacrylate,N,N-dimethylaminopropylmethacrylate, N,N-dimethylaminopropylacrylate,N-tert-butylaminopropylmethacrylate, N-tert-butylaminopropylacrylate andthe like. Exemplary amino(meth)acrylamides includeN-(3-aminopropyl)methacrylamide, N-(3-aminopropyl)acrylamide,N-[3-(dimethylamino)propyl]methacrylamide,N-(3-imidazolylpropyl)methacrylamide, N-(3-imidazolylpropyl)acrylamide,N-(2-imidazolylethyl)methacrylamide,N-(1,1-dimethyl-3-imidazoylpropyl)methacrylamide,N-(1,1-dimethyl-3-imidazoylpropyl)acrylamide,N-(3-benzoimidazolylpropyl)acrylamide, andN-(3-benzoimidazolylpropyl)methacrylamide.

Exemplary quaternary salts of the ionic monomers include, but are notlimited to, (meth)acrylamidoalkyltrimethylammonium salts (e.g.,3-methacrylamidopropyltrimethylammonium chloride and3-acrylamidopropyltrimethylammonium chloride) and(meth)acryloxyalkyltrimethylammonium salts (e.g.,2-acryloxyethyltrimethylammonium chloride,2-methacryloxyethyltrimethylammonium chloride,3-methacryloxy-2-hydroxypropyltrimethylammonium chloride,3-acryloxy-2-hydroxypropyltrimethylammonium chloride, and2-acryloxyethyltrimethylammonium methyl sulfate).

Other grafting monomers that can provide positively charged groups tothe surface of the substrate include the dialkylaminoalkylamine adductsof alkenylazlactones (e.g., 2-(diethylamino)ethylamine,(2-aminoethyl)trimethylammonium chloride, and3-(dimethylamino)propylamine adducts of vinyldimethylazlactone) anddiallylamine monomers (e.g., diallylammonium chloride anddiallyldimethylammonium chloride).

Functionalized substrates of the present invention may be prepared usingone of the above-described grafting monomers or a mixture of two or moreof the above-described grafting monomers to provide a functional groupfor further reaction with the ligand compounds and/or alter the surfaceproperties of a base substrate. When two or more of the above-describedgrafting monomers are used to alter the surface properties of a porousbase substrate, the monomers may be grafted onto the porous basesubstrate in a single reaction step (i.e., the two or more graftingmonomers are all present upon exposure to an electron beam) or insequential reaction steps (i.e., a first grafting monomer is presentupon a first exposure to an electron beam and a second grafting monomeris present upon a second exposure to the electron beam.

It will be understood that the grafting monomers may polymerize on thesurface of the substrate to yield a grafted polymer having pendantelectrophilic functional groups. These pendant electrophilic functionalgroups may then be further reacted with the ligand monomers of FormulasI and II to yield a grafted polymer having pendant ligand groups. Such apolymer may be depicted as Substrate˜(M_(ligand))_(m), where M_(lingand)represent a polymerized grafted monomer having pendant ligand groups,and m is at least two. Such polymers may further comprise other optionalgrafting monomers.

For radiation grafting, one embodiment of the method comprises:

1) providing a base substrate, preferably a porous base substrate havinginterstitial and outer surfaces;

2) imbibing the porous substrate with a first solution comprising (a)one or more grafting monomers having at least one acryloyl group and atleast one second electrophilic functional group, or a second functionalgroup that may be converted to an electrophilic functional group;

3) exposing the imbibed porous base substrate to ionizing radiation,preferably e-beam or gamma radiation, so as to form a firstfunctionalized substrate comprising a base substrate having graftedelectrophilic functional groups (from the grafting monomer) attached tothe surface(s) thereof; and

4) contacting the substrate having grafted electrophilic functionalgroups to the ligand compounds of Formula I or II to produce a substratehaving grafted ligand groups attached to the surface(s) thereof, asillustrated by Formulas III to XII.

In another embodiment, the imbibing step 2 may comprise imbibing thesubstrate with a grafting monomer having an electrophilic functionalgroup. This electrophilic functional group may be further functionalizedwith a compound having a nucleophilic functional group and a second,non-electrophilic group that may be converted to an electrophilic group.For example, a grafting monomer such as vinyl dimethylazlactone may begrafted to the surface of the substrate. This in turn may be reactedwith a nucleophilic compound such as allyl amine, the allyl group ofwhich is not reactive with the ligand compounds, by may be converted toan electrophilic group, such as a bromo group by reaction withN-bromosuccinimide or bromine water.

In some embodiments, the imbibing solution may comprise optionalgrafting monomers that may impart grafted ionic or hydrophilic groups tothe surface of the substrate. For example, optional grafting monomersmay comprise hydrophilic mono- and diacrylates of poly(ethylene oxide).

In another embodiment, the method comprises:

1) providing a porous base substrate having interstitial and outersurfaces;

2) imbibing the porous base substrate with a first solution to form animbibed porous base substrate, the first solution comprising (a) atleast one grafting monomer having an acrylate group and a photoinitiatorgroup and (b) one or more monomers having at least one acrylate groupand at least one additional ethylenically unsaturated, free-radicallypolymerizable group; and optionally (c) one or more additional monomershaving at least one free-radically polymerizable group and anelectrophilic group;

3) exposing the imbibed porous base substrate to a controlled amount ofelectron beam radiation so as to form a first functionalized substratecomprising grafted photoinitiator groups attached to the surfaces of theporous base substrate, and

4) optionally imbibing the substrate comprising grafted photoinitiatorgroups with an imbibing solution comprising a grafting monomer having anelectrophilic group;

5) exposing the porous base substrate comprising grafted photoinitiatorgroups to a controlled amount of UV radiation to polymerize or crosslinkthe remaining ethylenically unsaturated, free-radically polymerizablegroups and incorporating the grafting monomer having the electrophilicgroup, and

6) contacting the substrate having grafted electrophilic groups to theligand compounds of Formulas I and/or II,

wherein at least one of steps 2 or 4 contain a grafting monomer havingan electrophilic group.

Further reference regarding this method may be found in Assignee'scopending application U.S. 2009/0098359, incorporated herein byreference in its entirety.

The ionizing radiation grafting methods involve the irradiation ofsubstrate surfaces with ionizing radiation to prepare free radicalreaction sites on such surfaces upon which the monomers are grafted.“Ionizing radiation” means radiation of a sufficient dosage and energyto cause the formation of free radical reaction sites on the surface(s)of the base substrate. Ionizing radiation may include beta, gamma,electron-beam, x-ray and other forms of electromagnetic radiation. Insome instances, corona radiation can be sufficiently high energyradiation. The radiation is sufficiently high energy, that when absorbedby the surfaces of the base substrate, sufficient energy is transferredto that support to result in the cleavage of chemical bonds in thatsupport and the resultant formation of a free radical site on thesupport.

High energy radiation dosages are measured in kilograys (kGys). Dosescan be administered in a single dose of the desired level or in multipledoses which accumulate to the desired level. Dosages can rangecumulatively from about 1 kGys to about 100 kGys depending on the sourceof radiation. Generally, e-beam dosage is higher than gamma. Preferably,the cumulative dosage exceeds 30 kGys for substrates resistant toradiation damage when using e-beam. Doses in the range of 3 to 7 kGysare usually acceptable for all polymers when using gamma radiation.

Electron beam and gamma radiation are preferred for this method ofgrafting due to the ready-availability of commercial sources. Electronbeam generators are commercially available from a variety of sources,including the ESI “ELECTROCURE” EB SYSTEM from Energy Sciences, Inc.(Wilmington, Mass.), and the BROADBEAM EB PROCESSOR from PCT EngineeredSystems, LLC (Davenport, Iowa). Sources of gamma irradiation arecommercially available from MDS Nordion using a cobalt-60 high-energysource. For any given piece of equipment and irradiation samplelocation, the dosage delivered can be measured in accordance with ASTME-1275 entitled “Practice for Use of a Radiochromic Film DosimetrySystem.” By altering the source strength and the area spread variousdose rates can be obtained.

Further details of the radiation grafting methods may be found inAssignee's U.S. 2007/0154703 (Waller et al.), incorporated herein byreference in its entirety.

In one embodiment, the method provides an article having a grafted,ligand functionalized surface, comprising the reaction product of agrafted functional group and one or more ligand monomers. The method ofmaking a ligand functionalized substrate alters the original nature ofthe porous base substrate, as the grafted species include a ligandgroup. The present invention enables the formation of ligandfunctionalized substrates having many of the advantages of a basesubstrate (e.g., mechanical and thermal stability, porosity), but withenhanced binding specificity for biomolecules such as viruses, resultingfrom the monomers and steps used to form a given functionalizedsubstrate. The present invention reduces or eliminates many of the knownproblems associated with porous base substrates formed from hydrophilicpolymers including, but not limited to, hygroexpansive issues;brittleness without humidification problems; mechanical strengthweakness; and poor solvent, caustic and/or acidic resistance.

In one embodiment, the grafting monomer having optional hydrophilicgroups can be used to impart a hydrophilic character to a hydrophobicbase substrate, such as a PVDF substrate. These grafting monomers mayhave a hydrophilic poly(alkylene oxide) group.

Alternatively, optional grafting monomers may optionally contain anionic group. In these instances, hydrophilicity is imparted using amonomer, which may contain a grafting acrylate group or a non-acrylatepolymerizable group, and a hydrophilic group, such as a quaternaryammonium group. Such ionic groups may further impart enhancedselectivity to the functionalized substrate by repelling biologicalspecies having a like charge as the ionic group, at the appropriate pH.

The ligand-functionalized porous substrates are particularly suited asfilter media, for the selective binding and removal of viruses, such asendogenous or adventitious viruses, from biological samples. As theligand is grafted to the base substrate (either directly or indirectly),the ligand functionalized substrate is durable. The present disclosurethen further provides a method for the removal of viruses from avirus-containing sample, such as a biological sample comprisingcontacting a sample with the ligand functionalized substrate asdescribed herein.

The sample is contacted with the virus-capture membrane for a timesufficient to yield a log-reduction value (LRV) of at least 1.0 forneutral viruses disposed in the solution when the solution comprisesfrom 0 to about 50 mM salt, preferably to yield a log-reduction value(LRV) of at least 1.0 for neutral viruses disposed in the solution whenthe solution comprises from 0 to about 100 mM salt, and more preferablystill to yield a log-reduction value (LRV) of at least 1.0 for neutralviruses disposed in the solution when the solution comprises from 0 toabout 150 mM salt. It is still more preferred that the solution iscontacted with the virus-capture membrane for a time sufficient to yielda log-reduction value (LRV) of at least 5.0 for neutral viruses disposedin the solution when the solution comprises from 0 to about 50 mM salt,preferably to yield a log-reduction value (LRV) of at least 5.0 forneutral viruses disposed in the solution when the solution comprisesfrom 0 to about 100 mM salt, and more preferably still to yield alog-reduction value (LRV) of at least 5.0 for neutral viruses disposedin the solution when the solution comprises from 0 to about 150 mM salt.The term neutral virus is used to denote any virus that has anisoelectric point (pI) around 7, or optionally, nominally between 6 and8. Alternatively, the term “near-neutral” may be used. The samplesolution pH is such that the virus is negatively charged.

This importance of viral clearance in the presence of salt, known as“salt tolerance” is that many process solutions used inbiopharmaceutical manufacture have conductivities in the range of 15-30mS/cm. Salt tolerance is measured in comparison to the conventional Qligand (AETMA, 2-aminoethyltrimethylammonium chloride), which rapidlyloses capacity for some viruses (e.g., φ X174) at conductivities three-to six-fold less than the target range, e.g. dropping viral clearancefrom a six log-reduction value (LRV) to a one log-reduction value (LRV)in going from 0 to 50 mM NaCl. Viruses such as φ X174 and PM2 have pIsclose to 7, (pI for φ X174: 6.6; for PM2: 7.3; for poliovirus type 1:7.5 (Brunhilde strain) and are neutral or near-neutral.

In many embodiments, the substrate may be functionalized so that otherproteins are excluded or repelled from the ligand functionalizedsubstrate, while viruses and other negatively charged species such ashost cell proteins, DNA, etc. bind to the ligand functional group. Inaddition, as previously described, the substrate may be directly orindirectly grafted with one or more ionic monomers. In particular, theporous substrate may comprise grafted ionic groups that are positivelycharged at the selected pH of the biological sample solution to causeelectrostatic charge repulsion of proteins, such as monoclonalantibodies, many of which are charged positive at neutral pH.

Preventing protein binding, such as mAb binding, can be accomplished byincreasing the pKa of the ligand, or grafting an additional positivelycharged functional group, and adjusting the pH of the solution so thatthe mAb and ligand are both charged positive during loading. This causeselectrostatic charge repulsion of the mAb from the ligand and substratesurface. The virus, in contrast, is normally negatively charged andbinds to the ligand. Most therapeutic mAbs tend to have pI's between 8and 10. Thus, mAbs are positively charged at neutral pH, which preventstheir binding to substrate surface. Viruses, on the other hand, can havea variety of pI's and many have pI's below 7. Therefore the pH of thesample solution should be maintained below the isoelectric point of theprotein of interest (such as a mAb) and above the isoelectric point ofthe virus.

The ligands and other grafted functional groups herein are selectedbased on the above criteria and outcomes, i.e., it is salt tolerant andhas a high pKa (e.g., >10) causing electrostatic charge repulsion of themAb. The ligand is immobilized on a porous membrane and thevirus-containing fluid flows through the membrane while the virus istrapped by the ligand.

In some embodiments, the grafted article containing the bound virus isdisposable. In such embodiments, the binding of the virus to the filtermedium is preferably essentially irreversible because there is no needto recover the bound virus. Nonetheless, one can reverse the binding ofviruses by increasing the ionic strength of an eluting solution. Incontrast, for many instances of protein binding, the binding phenomenonmust necessarily be reversible or the desired protein cannot be elutedfrom the column.

The substrate for viral capture may be any previously described, but ispreferably a microporous membrane. The membrane pore size desired isfrom 0.1 to 10 μm, preferably 0.5 to 3 micrometers and most preferably0.8 to 2 micrometers. A membrane with a high surface area for theinternal pore structure is desired, which typically corresponds to finepore sizes. However, if the pore size is too small, then the membranetends to plug with fine particulates present in the sample solution.

If desired, efficiency of viral binding and capture may be improved byusing a plurality of stacked, ligand-functionalized porous membranes asa filter element. Thus the present disclosure provides a filter elementcomprising one or more layers of the porous, ligand functionalizedsubstrate. The individual layers may be the same or different, and mayhave layers of different porosity, and degree of grafting by theaforementioned grafting monomers. The filter element may furthercomprise an upstream prefilter layer and downstream support layer. Theindividual filter elements may be planar or pleated as desired.

Examples of suitable prefilter and support layer materials include anysuitable porous membranes of polypropylene, polyester, polyamide,resin-bonded or binder-free fibers (e.g., glass fibers), and othersynthetics (woven and non-woven fleece structures); sintered materialssuch as polyolefins, metals, and ceramics; yarns; special filter papers(e.g., mixtures of fibers, cellulose, polyolefins, and binders); polymermembranes; and others.

In another embodiment, there is provided a filter cartridge includingthe above-described filter element. In yet another embodiment, there isprovided a filter assembly comprising the filter elements and a filterhousing. In a further embodiment, this invention relates to a method ofviral capture comprising the steps of:

a) providing the filter element comprising one of more layers of theligand functionalized base substrate of this disclosure, and

b) allowing a moving biological solution containing a virus to impingeupon the upstream surface of the filter element for a time sufficient toeffect binding of a virus.

The present invention is described above and further illustrated belowby way of examples, which are not to be construed in any way as imposinglimitations upon the scope of the invention. On the contrary, it is tobe clearly understood that resort may be had to various otherembodiments, modifications, and equivalents thereof which, after readingthe description herein, may suggest themselves to those skilled in theart without departing from the spirit of the present invention and/orthe scope of the appended claims.

EXAMPLES Materials

Polyethyleneimine of M_(w) of about 25,000 was purchased from AlphaAesar (Ward Hill, Mass.).

Polyhexamethylene biguanide of M_(w) of about 25,000 was purchased fromArch Chemical (South Plainfield, N.J.).

Regenerated cellulose (RC) discs with a pore size of 0.45 μm, diameterof 25 mm and average thickness of 180 μm were obtained as type 184 fromSartorius, Germany.

PVDF film; a TIPS (thermally-induced phase separation) porous film, 5mils thick, with a Gurley (air flow) about 4.5 sec/50 cc air, bubblepoint pore size of about 1.9 microns, 1.4 μm average pore size, 72%porous, and a water flux time of about 10 sec (using 100 ml water, 47 mmPall Gelman Filter Funnel 4238, at 23 in Hg vacuum). Reference may bemade to U.S. Pat. No. 7,338,692 (Smith et al.).

“VAZPIA” refers to 2-propenoylaminoethanoic acid, 2-(4-(2-hydroxy-2methylpropanoyl)phenoxy)ethyl ester prepared according to Example 1 ofU.S. Pat. No. 5,506,279 (Babu et al.).

“PEG 400 diacrylate” diacrylate ester of polyethyleneglycol, molecularweight 400, Aldrich Chemical Co.

Testing of Membranes: Dye Assay:

RC membranes derivatized with amine ligands were tested for relativeionic capacity colorimetrically by reaction with a negatively chargedorange dye. Tropaeolin O (Acros, Geel, Belgium) was dissolved in 66%(v/v) ethanol to a concentration of 0.5 mg/mL. RC membranes were rinsedin 20% ethanol then incubated in the Tropaeolin O solution for 4 hr at22° C. The membranes were then removed from the dye solution and washedthoroughly with 20% ethanol to remove unbound dye. A blank RC membranewas used as a control to eliminate the effects of any potentialnon-specific binding. Finally, the color (a*) of the stained membraneswas measured using a Color Quest colorimeter (HunterLab, Reston, Va.).

Binding of Bovine Serum Albumin:

The membranes were analyzed for binding of proteins by passing solutionsof the test analytes through a 6-layer stack of the membranes punchedout into 25-mm diameter discs placed in a 25 mm diameter holder attachedto an AKTA chromatography system (GE Healthcare, N.Y.). Feed solutionwas prepared by dissolving bovine serum albumin (BSA) in 50 mM bisTrisbuffer pH 6 to a concentration of 0.2 mg/mL as determined by absorbanceat 280 nm. BSA feed solution was pumped through the membrane adsorber ata flow rate of 5 mL/min until complete breakthrough was observed viaabsorbance at 280 nm. The dynamic binding capacity of the membrane wasevaluated using standard chromatography techniques.

Determination of Viral Capture:

Viral capture was measured using a standard protocol developed at theFood and Drug Administration as described in the PDA Technical Report 41(TR41), Virus Filtration. The test virus was a bacteriophage φX174. Astandard stock solution containing 10⁹ to 10¹² pfu/ml (plaque formingunits) in a 10 mM TRIS-HCl buffer at pH 7.5, with NaCl concentration of0, 50 and 150 mM was prepared. This stock was flowed through themembrane stack as previously described. During loading, 50 mL ofchallenge solution was pumped through the membrane adsorber at a flowrate of 5 mL/min and flow-through samples were collected every 10 ml.The effluent was collected as 1 ml fractions using a fraction collector.Fractions corresponding to a total throughput of 10 ml, 20 ml, 30 ml, 40ml and 50 ml through the membranes were taken aside and these weresubjected to several decadal dilutions. The virus stock solution wasalso subjected to a similar dilution series. The diluted fractions werethen incubated with E coli solution and plated onto agar plates alongwith growth medium comprised of tryptic soy broth. The inverted plateswere incubated overnight and the numbers of plaques were counted. TheLRV (or log reduction in viral load) was estimated from knowledge of thecorresponding dilution factor as well as the initial concentration ofthe phage and calculated using Eqn (1):

$\begin{matrix}{{L\; R\; V} = {\log_{10}\left( \frac{{Titer}_{challenge}\left( {p\; f\; u\text{/}{mL}} \right)}{{Titer}_{sample}\left( {p\; f\; u\text{/}{mL}} \right)} \right)}} & (1)\end{matrix}$

Example 1 and 2 Part A: Preparation of Substrate Membranes HavingGrafted Electrophilic Groups

Grafting of the amine-containing ligands to the RC base membrane waseffected by the following method. First, hydroxyl groups on thecellulose substrate were activated by reacting the membranes in a 5%allyl glycidyl ether (as the grafting compound) solution in 30% sodiumhydroxide overnight at 22° C. The covalently attached allyl groups wereconverted to electrophilic bromo groups by bromination using a 10 g/Lsolution of N-bromosuccinimide for 2 hr.

Part B: Grafting of Functional Groups on Activated Membranes

Grafted bromo groups on the membranes made in Part A were replaced withamine ligands via nucleophilic substitution in which brominatedmembranes were reacted with amine ligand solution for 2 days at 22° C.to ensure high levels of amine substitution. Ligand solutions were asfollows: 10% (w/w) solids in aqueous solution pH 11 for thepolyethyleneimine (PEI) and polyhexamethylene biguanidine (PHMB). TheBSA capacity, and ΦX174LRV clearance at three salt levels are shown inTable 1.

TABLE 1 BSA Capacity ΦX174LRV Ligand (mg/mL) 0 mM NaCl 50 mM NaCl 150 mMNaCl PHMB 8 ± 1 8.8 ± 0.3 8.5 ± 0.9 7.1 ± 0.1 PEI 6.1 ± 0.6 8.7 ± 0.36.1 ± 0.4 5.8 ± 0.8 ¹Values reported as means ± SD, n = 2.

Example 3

The PVDF porous substrate was imbibed with a solution containing 10.0wt. % PEG 400 diacrylate monomer available from Sartomer Inc. of Exton,as PA SR344™ and 90.0 wt. % methanol. The coated porous substrate wasthen ‘wet’ between two layers of PET film (first layer and second layer)having a thickness of approximately 100 micrometers. A removable firstlayer and a removable second layer were each placed on opposite sides ofthe coated porous substrate with any excess solution and trapped airbubbles squeezed out with a hand held rubber roller. The multilayerstructure was conveyed through the electron beam on a carrier web. Themultilayer structure was irradiated by electron beam (E-beam) on an ESICB-300 electron beam with a dose of 20 kGy set at a voltage of 300 keV.Two minutes following irradiation, the hydrophilic functionalized poroussubstrate was removed from the first and second PET layers. The membranewas soaked in a tray of water that was exchanged three times with DIwater to wash the membrane of unreacted monomer and subsequently airdried.

The hydrophilic PVDF porous substrate was coated in a solutioncontaining 10.0% vinyl dimethylazlactone-allyl amine adduct in 20% DIwater, and 70% methanol. The solution filled membrane is again subjectedto an E-beam dose of 40 kGy set at a voltage of 300 keV, which alsografts this monomer to the surface of the PVDF substrate. After twominutes, the PET sandwich was opened and the grafted PVDF membrane wassoaked in a tray of water that was exchanged three times with DI waterto wash the membrane of unreacted monomer and subsequently air dried. Inaddition to the grafted PEG diacrylate, it is believed that the vinyldimethylazlactone-allyl amine adduct,CH₂═CH—(CO)NHC(CH₃)₂(CO)NH—CH₂—CH═CH₂, may be directly grafted to thesurface of the substrate; i.e.:substrate-CH₂CH₂—(CO)NHC(CH₃)₂(CO)NH—CH₂—CH═CH₂, allowing terminal allylgroups for conversion to electrophilic terminal bromo groups(—CH₂CH₂CH₂Br and/or —CH₂CHBrCH₃), for subsequent reaction with theligand compound. Upon grafting, the dimethylazlactone-allyl amine adductmay also polymerize to produce a grafted acrylate polymer having aplurality of pendant —(CO)NHC(CH₃)₂(CO)NH—CH₂—CH═CH₂ groups, which mayalso be converted to terminal bromo groups. The dimethylazlactone-allylamine adduct may also polymerize with any unreacted acrylate groups fromthe PEG diacrylate.

A 6 inch×7 inch sample of allyl-functional PVDF membrane was placed in a500 ml polyethylene bottle and covered with 500 mL of a 10 gram/Lsolution of N-bromosuccinimide in deionized water. The bottle was sealedand the mixture was allowed to stand at ambient temperature overnight.The excess solution was poured off, and the membrane was washed under astream of deionized water for 30 minutes. The bottle was then filledwith a solution of 10% by weight polyethyleneimine (PEI) in deionizedwater, the bottle was sealed, and the mixture was tumbled end-over-endat ambient temperature for 4 days. The excess solution was decanted, thebottle was filled with deionized water, allowed to stand for 30 minutes,and decanted again. This process was repeated an additional 4 times tothoroughly wash the derivatized membrane, then the membrane was allowedto air dry.

Example 4

The following Example used the general procedures described inApplicant's copending application U.S. 2009/0098359, incorporated hereinby reference its' entirety.

The PVDF porous substrate was imbibed with a solution containing 10.0wt. % PEG 400 diacrylate monomer available from Sartomer Inc. of Exton,Pa. as SR344™ and 90.0 wt. % methanol. The coated porous substrate wasthen placed ‘wet’ between two layers of PET film (first layer and secondlayer) having a thickness of approximately 100 micrometers. A removablefirst layer and a removable second layer were each placed on oppositesides of the coated porous substrate with any excess solution andtrapped air bubbles squeezed out with a hand held rubber roller. Themultilayer structure was conveyed through the electron beam on a carrierweb. The multilayer structure was irradiated by electron beam (E-beam)on an ESI CB-300 electron beam with a dose of 20 kGy set at a voltage of300 keV. Two minutes following irradiation, the hydrophilicfunctionalized porous substrate was removed from the first and secondPET layers. The membrane was soaked in a tray of water that wasexchanged three times with DI water to wash the membrane of unreactedmonomer and subsequently air dried to produce a substrate giving graftedhydrophilic poly(ethylene oxide) groups.

Two functional polymerizable free radical active monomers comprising 1%VAZPIA photoinitiator and 5% 3-(Acryloxy)-2-hydroxypropylmethacrylate(Ac-Mac) are combined in methanol to make a coating solution that isimbibed into the hydrophilic PVDF membrane of Step 1 using the sameprocedures. The solution filled membrane is again subjected to an E-beamdose of 40 kGy set at a voltage of 300 keV, which also grafts thesemonomers to the surface of the PVDF substrate. After two minutes, thePET sandwich is opened and the grafted PVDF membrane is then allowed toair dry and not washed to produce a membrane having graftedphotoinitiator groups and grafted methacrylate groups.

Ac-Mac, having a faster reacting acrylate monomer moiety ispreferentially grafted to the support surface using the E-beam process.This allows most of the slower methacrylate moiety of AC-Mac to be freefor later polymerization with the UV process. The photoinitiator VAZPIAis also grafted in Step 2. Therefore, these grafted chains have freeradical active moieties and photoinitiator moieties on the same chain.In the third functionalizing step, a coating solution containing 10.0%vinyl dimethylazlactone-allyl amine adduct in 20% DI water, and 70%methanol was imbibed into the grafted TIPS PVDF microporous membrane ofSteps 1 & 2. The porous film again was sandwiched “wet” between PET filmand closed with any excess solution or trapped air bubbles removed witha roller. The sample was then UV irradiated using Quantum Technologies(Quant 48) system using UVA lamps and run under the UV processor at aspeed of about one foot per minute (4 feet exposure length, single sideat 31 mW/cm²). The sample sandwich was turned over and run again at thesame speed. After UV irradiation, the grafted porous membrane wasremoved from the sandwich and was washed by soaking it in a tray ofwater and exchanging it with clean water three times. The functionalizedmembrane was allowed to air dry. The resultant membrane has grafteddimethylazlactone-allyl amine adduct groups grafted to the surface ofthe substrate. Such grafting may be initiated by the free radicalgenerated from the grafted photoinitator monomer, or from themethacrylate group of the grafted AcMac monomer. Again, thedimethylazlactone-allyl amine adduct may produce a grafted acrylatepolymer having pendant —(CO)NHC(CH₃)₂(CO)NH—CH₂—CH═CH₂ groups from eachacrylate polymer unit.

A 6 inch×7 inch sample of allyl-functional PVDF membrane was graftedwith PEI according to the procedure of Example 3.

Examples 5-6

The PVDF porous substrate was imbibed with a solution containing 10.0wt. % PEG 400 diacrylate monomer, SR-344™ and 90.0 wt. % methanol. Thecoated porous substrate was then placed ‘wet’ between two layers ofpolyethylene terephthalate (PET) film (first layer and second layer)having a thickness of approximately 100 micrometers. A removable firstlayer and a removable second layer were each placed on opposite sides ofthe coated porous substrate with any excess solution and trapped airbubbles squeezed out with a hand held rubber roller. The multilayerstructure was conveyed through the electron beam on a carrier web. Themultilayer structure was irradiated by electron beam (E-beam) on an ESICB-300 electron beam with a dose of 20 kGy set at a voltage of 300 keV.Two minutes following irradiation, the hydrophilic functionalized poroussubstrate was removed from the first and second PET layers. The membranewas soaked in a tray of water that was exchanged two times withdeionized water to wash the membrane of unreacted monomer andsubsequently air dried

The resulting hydrophilic membrane was then grafted a second time byeach of the two alternate procedures:

Direct. The membrane was re-sandwiched and imbibed with a 20% solutionof glycidyl methacrylate in methanol and passed through the electronbeam, receiving a dose of 40 kGy at an accelerating voltage of 300 kV.The grafted membrane was removed and washed twice in isopropanol anddried.

Indirect. The membrane was inserted into a Ziploc bag in a glove box andsealed under an atmosphere of less than 40 ppm oxygen. The sealed bagwas removed from the glove box and passed through the electron beam,receiving a dose of 40 kGy at a voltage of 300 kV. The sealed bag wasre-conveyed into the glove box, opened under an atmosphere of less than40 ppm oxygen and the membrane removed and placed into another,unirradiated Ziploc bag and imbibed with sufficient 20% glycidylmethacrylate (GMA) in methanol solution to wet the membrane. The bag wassealed to prevent evaporation and the imbibed membrane was allowed tosit for a period of 4 hours before being removed and washed twice inisopropanol and dried.

Approximately 6 inch×7 inch samples of oxirane-functional PVDF membraneswere reacted with PEI by reaction with a 10% by weight solution of PEIin deionized water for 24 hours, then washed as indicated in Example 3and allowed to air dry.

ΦX174 Clearance at 150 mM NaCl Example Description ΦX174 LRV 3 PEI/VDMallyl 8.0 4 PEI/VDM allyl 8.1 5 PEI/GMA (indirect) 6.3 6 PEI/GMA(direct) 8.2 LRV results for the 50 mL fraction

1. An article comprising a substrate and extending from the surfacesthereof grafted biguanide ligand groups.
 2. The article of claim 1,wherein said biguanide ligand groups are one or more of the formula:

wherein R² is an arylene or alkylene and a is at least one.
 3. Thearticle of claim 1, further comprising grafted quaternary ammoniumgroups on the surface of the substrate.
 4. The article of claim 1,wherein the substrate is a porous substrate.
 5. The article of claim 4,wherein the porous substrate is selected from a porous membrane, porousnon-woven web, or porous fiber.
 6. The article of claim 1, wherein thesubstrate is a thermoplastic polymer.
 7. The article of claim 1, whereinthe grafted biguanide ligand groups comprise the reaction product of (a)a first grafted electrophilic functional group comprising an epoxygroup, an isocyanato group, or an azlactone group with (b) a ligandcompound:

wherein each R⁴ is individually H, alkyl or aryl, each R⁶ isindividually alkylene or arylene, c may be zero or an integer from 1 to500, and d is zero or 1, with the proviso that when d is zero, then c is1 to
 500. 8. An article comprising a porous base substrate havinginterstitial and outer surfaces; and grafted ligand groups extendingfrom the surfaces of the porous base substrate, wherein the graftedligand groups comprise the reaction product of a grafted electrophilicfunctional group and a ligand compound:

wherein each R⁴ is individually H, alkyl or aryl, each R⁶ isindividually alkylene or arylene, c may be zero or an integer from 1 to500, and d is zero or 1, with the proviso that when d is zero, then c is1 to
 500. 9. The article of claim 8, wherein the grafted electrophilicfunctional group is selected from (i) an epoxy group or a ring-openedepoxy linkage group, (ii) an azlactone group or a ring-opened azlactonelinkage group, or (iii) an isocyanato group.
 10. The article of claim 8,further comprising grafted ionic or hydrophilic groups.
 11. The articleof claim 10, wherein the grafted ionic groups are grafted quaternaryammonium groups.
 12. The article of claim 8, wherein the porous basesubstrate is microporous.
 13. The article of claim 8, wherein thearticle further comprises grafted hydrophilic groups.
 14. The article ofclaim 8, wherein the porous base substrate comprises a porous membrane,a porous nonwoven web, or a porous fiber.
 15. The article of claim 8,wherein the grafted ligand groups comprise the reaction product of (a) afirst grafted electrophilic functional group comprising an epoxy group,an isocyanato group, or an azlactone group with (b) a ligand compound:

wherein each R⁴ is individually H, alkyl or aryl, each R⁶ isindividually alkylene or arylene, c may be zero or an integer from 1 to500, and d is zero or 1, with the proviso that when d is zero, then c is1 to
 500. 16. A method of preparing a ligand functional substratecomprising: 1) providing a thermoplastic polymer substrate; 2) graftinga functional group to the surface of the substrate to produce asubstrate having a grafted electrophilic functional groups extendingfrom the surface(s) thereof; and 3) reacting the grafted electrophilicfunctional groups with biguanide ligand groups to produce a substratehaving grafted biguanide ligand groups extending from the surface(s) ofthe substrate.
 17. The method of claim 16, comprising the steps of: a)providing a porous thermoplastic polymer base substrate; b) imbibing theporous thermoplastic polymer base substrate with a first solution toform an imbibed porous base substrate, the first solution comprising atleast one grafting monomer having (a) a free-radically polymerizablegroup and (b) an additional electrophilic functional group; c) exposingthe imbibed porous base substrate to a controlled amount of electronbeam radiation so as to form a first functionalized substrate havinggrafted electrophilic functional groups; d) reacting the functionalizedsubstrate having grafted electrophilic functional groups with a ligandcompound:

wherein each R⁴ is individually H, alkyl or aryl, each R⁶ isindividually alkylene or arylene, c may be zero or an integer from 1 to500, and d is zero or 1, with the proviso that when d is zero, then c is1 to
 500. 18. The method of claim 17, wherein the imbibing solutionfurther comprises a second grafting monomer having (a) a free-radicallypolymerizable group and (b) an ionic group or a hydrophilic group. 19.The method of claim 18, further comprising the steps of: imbibing thefirst functionalized substrate with a second solution to form a firstimbibed functionalized substrate, the second solution comprising atsecond grafting monomer having (a) a free-radically polymerizable groupand (b) a second quaternary ammonium group, and exposing the firstimbibed functionalized substrate to a controlled amount of electron beamradiation so as to form a second functionalized substrate comprisinggrafted quaternary ammonium groups attached to the surfaces of theporous base substrate.
 20. The method of claim 16, wherein the biguanideligand groups are one or more of the formula:

wherein R² is an arylene or alkylene and a is at least one.